As is known, the critical requirements for preserving fresh perishable products are maintaining the temperature as close as possible to the maximum freezing point, which is typically below 0° C., maintaining the humidity at values above 90%, and absence of ventilation.
As is known, the variation of the coefficients of deterioration as the preservation parameters vary is not linear with the variation and interaction thereof, so that for example, when using the typical values of a conventional or industrial refrigerator, there is on average a temperature which oscillates from +2 to +5° C., with a relative humidity of approximately 60% and an internal ventilation, and therefore the deterioration coefficient is greater than 5, thus reducing to less than one fifth the useful life of the products.
Currently commercially available refrigerators are typically provided with a preservation compartment, which is thermally insulated and inside or in contact with which there is an evaporation circuit, constituted by a coil or plate, which is connected to a compressor so that in the evaporation circuit that is present inside the refrigerator there is a direct expansion of the gas, so that one is in the presence of temperatures which are significantly lower than the temperature values of such preservation compartment, such temperature difference being normally over 10° C.
The temperature inside the preservation compartment is regulated by a thermostat, and therefore operation of the refrigerator is of the on-off type.
This type of operation causes extreme dehydration of the air due to the high ΔT between the temperature of the evaporating gas and the environment, with consequent desiccation of the preserved products; moreover, there are continuous oscillations of the temperature inside the preservation compartments due to the type of operation of the compressor.
The use of a thermostat introduces the need to adjust the temperature inside the preservation compartment, so as to take into account the hysteresis of the thermostat and its precision.
The type of construction and operation inevitably causes unevenness in the temperature inside the compartment, and moreover, due to the great differential in temperature between the air and the evaporating gas, one has a surface at a negative temperature, which in case of direct contact with the fresh products damages them by freezing.
Another problem further consists in that the energy consumption of a conventional refrigerator is concentrated predominantly in the warm hours of the day, which correspond to the overload periods of electrical mains.
Another problem further consists in that, particularly for fresh products, if the electric power supply is not available, there is a rapid temperature variation which damages the product.